I'm getting ready to mount my solar panels to my 5ver roof. It's 3/8" plywood. I'm planning two screws per bracket and four brackets per panel. I bought stainless steel screws for the mounting and plan to screw the bracket directly to the plywood through the rubber roof as many have done before me. This morning I got to thinking about the mounting and realized I had purchased sheet metal screws.Need your feedback on sheet metal screws vs. wood screws. Obviously additional screws are very little cost so that's not the issue. Just wondering if the wood screws will hold better.Any issue with using the sheet metal screws instead of wood screws?

I prefer sheet metal screws to wood screws, but have no technical basis for that opinion other than they seem easier to screw in without splitting the wood. Otherwise, I mostly use deck screws for wood projects. I almost always pre-drill the holes.

I had heard that metal screws can be used in place of wood screws, but not the other way around.

I would use Star head or Square head WOOD screws.And more importantly, screws are a very effective way of channeling water into materials. To protect your roof do what is common on Sailboats and other yachts.Drill a small pilot hole for the screw and fill it with silicone sealant. Then insert your screw. after the screws are in cover them with more sealant. I would also put sealant under the "feet" or mounting bracket of the panels.This should seal the threads and under the head and not allow water ingress.You definitely do not want water getting in to the plywood structure of your roof.

The prospect of drilling holes in the roof gives me the heebie-geebies. But, if'n it was me, I'd use a heavy sheet metal screw with a large pan head for secure contact with the metal bracket.

Here is what most people don't realize about screws is that they are supposed to work like a bolt. A bolt slips through the item to be secured then into a nut that tightens things together. A screw should be applied the same way. The screw slips through the item to be secured then into the wood or other material that will act as a bolt. Wood screws have a neck that facilitate the slipping through the item to be secured. A sheet metal screw needs a clearance hole in the item to be secured, which is usually thin a therefore does not need a neck.Sheet metal or drywall screws are IMO the most misused screw, I see wo 2x4's attached with drywall screws that have a space between them. That's because the first 2x4 acts like a nut then spins trying to drill a hole in the second one (the gap) an then taps into the 2x4.Sorry for the rant, this is a pet peeve of mine!Yes filling a pretty drilled screw hole with a sealant is the best way on the exterior of a RV.

Sheet Metal Screws vs. Wood Screws | Good Sam Community

48 Replies

DrewE
Explorer II
Feb 09, 2017
Vintage465 wrote:
Boon Docker wrote:
^ Best thing to use if you got them.

I'm sure they could be sourced or ordered from Samlex

Or Home Depot or Lowes or myriad other places...while not exactly everyday hardware, they are not difficult to find if one looks. It's not a Samlex-specific doohicky.
Vintage465
Nomad
Feb 09, 2017
Boon Docker wrote:
^ Best thing to use if you got them.

I'm sure they could be sourced or ordered from Samlex
Boon_Docker
Explorer III
Feb 09, 2017
^ Best thing to use if you got them.
Vintage465
Nomad
Feb 09, 2017
With my Samlex Solar panels, they came with these really nifty rubberized expanding fasteners

This is what it looks like completed. I would put some silicone sealant around that dude when you insert it in the 1/2" hole. and I would put some on the threads when you tighten it.

I think unless you're getting into a joist or truss this is the way to go.
Cameo_Phil
Explorer
Feb 08, 2017
I suggest that you use Dicor sealant and not use silicone. Silicone will eventually fail and additional silicone will not adhere to the original silicone.
Durb
Explorer
Feb 08, 2017
"No one uses true "WOOD" screws any longer"

I do. I have a full set of Screw-Sinks along with boxes of the corresponding size screws. The Screw-Sink drills a pilot hole and clearance hole plus will counterbore for a plug. I wax the screws before installing. Perfect for work on nice pieces.

However, a pan head or truss head sheet metal screw is what I would use for that application.
Dusty_R
Explorer
Feb 08, 2017
I do a little duct work/heating. I like to use self piercing screws, up through 26ga. when the sheet metal heaver than that I go to self drilling screws.

Dusty
dockmasterdave
Explorer
Feb 08, 2017
Wood screw #1

Wood screw #2

Either of these would work for this application depending on his bracket.
Notice they are wood screws, with a deeper, more coarse thread than a sheet metal screw, and are threaded all the way to the head.
If someone wants to make a clicky, go for it.
Moderator edit to make URL's into clickys.
Cummins12V98
Explorer III
Feb 08, 2017
dockmasterdave wrote:
Are you a professional wood worker?

Yes sir. I was a general contractor for several years in PA before going into furniture building. I have built homes from the ground up, doing all of the work ourselves, except masonry.
I have been doing, nothing but, extremely high end custom furniture, since 1979. I also work on custom yacht interiors.
I meant no disrespect.
I would be happy to send you a link to my business pages , if you would like. If so please PM me.

Must be a West Coast thing VS East Coast thing. I have NEVER used a true wood screw in any cabinet installation/fabrication or any other wood working project. 35+ years Carpenter/Superintendent building Medical/Dental Clinics Tenant Improvement or from the ground up. No disrespect here either!

Yes the op should be using a sheet metal fully threaded screw for his application. A #10 or larger but pre drill with a smaller hole.
BobsYourUncle
Nomad
Feb 08, 2017
The application here is going into 3/8 plywood. Not much wood for a screw to bite into. Gotta have threads right to the top of the screw.

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Sheet Metal Screws vs. Wood Screws

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